Color cathode ray tube display device and method of eliminating the influence of an external magnetic field

Abstract

A color cathode ray tube display device comprises a color cathode ray tube including a neck portion (1a), a funnel portion (1b), and a panel portion (1c), a compensating coil (7) which generates a compensating magnetic field for eliminating the influence of an external magnetic field that acts vertically on electron beams which will intersect a display screen of the color cathode ray tube (1), a current supply unit (4,5) for passing a sawtooth current synchronized with the vertical deflection cycle of a video signal into the compensating coil (7) so that the compensating coil generates the compensating magnetic field, and a memory (5b) for storing information about the sawtooth current passing through the compensating coil (7).

What is claimed is: 
     
       1. A color cathode ray tube display device comprising: a color cathode ray tube including a neck portion, a funnel portion, and a panel portion;   a compensating coil which generates a compensating magnetic field for eliminating the influence of an external magnetic field that acts vertically on electron beams which will intersect a display screen of said color cathode ray tube;   a current supply means for passing a sawtooth current synchronized with a vertical deflection cycle of a video signal into said compensating coil so that said compensating coil generates said compensating magnetic field; and   a memory for storing information about the sawtooth current passing through said compensating coil.   
     
     
       2. The color cathode ray tube display device according to claim 1, wherein said compensating coil is disposed in the vicinity of the panel portion of said cathode ray tube such that said compensating coil is wound around the panel portion. 
     
     
       3. The color cathode ray tube display device according to claim 2, wherein said compensating coil wound in the vicinity of the panel portion is attached to said color cathode ray tube. 
     
     
       4. The color cathode ray tube display device according to claim 2, wherein said compensating coil wound in the vicinity of the panel portion is attached to a box containing said color cathode ray tube therein. 
     
     
       5. The color cathode ray tube display device according to claim 1, wherein said compensating coil is disposed in the vicinity of the funnel portion of said cathode ray tube such that said compensating coil is wound around the funnel portion. 
     
     
       6. The color cathode ray tube display device according to claim 5, wherein said compensating coil wound in the vicinity of the funnel portion is attached to said color cathode ray tube. 
     
     
       7. The color cathode ray tube display device according to claim 5, wherein said compensating coil wound in the vicinity of the funnel portion is attached to a box containing said color cathode ray tube therein. 
     
     
       8. A method of eliminating the influence of an external magnetic field acting vertically on electron beams which intersect a display screen of a color cathode ray tube, comprising the steps of: disposing a compensating coil which can generate a compensating magnetic field for eliminating the influence of the external magnetic field;   after making convergence and purity adjustments to said cathode ray tube, passing a sawtooth current synchronized with a vertical deflection cycle of a video signal into said compensating coil so that said compensating coil generates the compensating magnetic field so as to exert moving forces which act in an identical direction on electron beams which will intersect an upper region and a lower region of the display screen of said color cathode ray tube;   moving electron beams which will intersect the upper region and lower region of the display screen of said color cathode ray tube in the same direction by means of the compensating magnetic field, thereby correcting displacements of the electron beams from corresponding phosphor dots on the display screen of said color cathode ray tube; and   storing information about the sawtooth current used for the correction into a memory.